Atomic-level evolution of lattice variation and strontium redistribution in Sr-δ-doped La2CuO4
By using atomic layer-by-layer oxide molecular beam epitaxy, Sr-δ-doped La2CuO4 (LCO) multilayered structures, in which some atomic layers of LaO have been fully substituted by SrO layers, have been fabricated. By varying the spacing between the LCO and SrO layers high-Tc superconductivity (≈ 40 K) has been obtained. The local variation of in-plane and out-of plane atomic lattice parameters and the strontium redistribution in multilayers grown on a LaSrAlO4 (LSAO) substrate are investigated in this study. more
Investigation of the chemistry of structural defects in Cu(In,Ga)Se2 solar cell material
Cu(In,Ga)Se2 (CIGSe) based solar cells fabricated with multi-stage co-evaporation show power-conversion efficiencies of more than 20%. However, in some cases efficiencies fall below this value, in particular when the solar cell is manufactured using low-temperature processing without a Cu-rich stage. The reasons for this efficiency loss, as well as the limitations for further efficiency increase, are not fully understood. In this project, we analyse structural defects in CIGSe absorber layers to gain a better understanding of the defects’ chemical characteristics. more
Octahedral distortion and chemistry at interfaces of oxide heterostructures
Oxide materials exhibit a wide range of ionic and electronic phenomena such as superconductivity, magnetism, ferroelectricity, thermoelectricity, etc. The crystal structure of oxides (generally perovskite or a derivative) is highly adaptable to changes in composition and this compatibility provides the opportunity of combining multiple oxides into heterostructures. Our aim is to reveal the atomic and electronic structure of the heterostructure interfaces using various Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) techniques. more
Cerium Reduction at the Interface between Ceria and Yttria-stabilised Zirconia and Implications for Interfacial Oxygen Non-stoichiometry
CeO2 and Y2O3-stabilized zirconia (YSZ) are two candidates for electrolyte materials in solid oxide fuel cells because of their high ion conductivities. Recent experiments have shown that hetero-structures consisting of alternating layers of Gd-doped CeO2 and YSZ exhibit even higher ionic conductivity than either of the bulk materials. In this project, we investigate the structure and chemistry of interfaces between CeO2 and YSZ using scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). more

Previous Research Topics

We study the strain and elemental distribution in La2/3Sr1/3MnO3 (LSMO) doped with ZrO2 using analytical TEM techniques. ZrO2 forms non-magnetic nanoparticles that introduce anomalous magnetic anisotropy and modifications to the electric transport properties of the LSMO thin film. Using electron energy-loss spectroscopy (EELS) in a probe-aberration-corrected JEOL JEM-ARM200CF, the atomic resolution elemental distribution of La, Sr, Mn, Zr and O, and the Mn valence state variation at the interface between LSMO and ZrO2 are observed. more
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